Thin film transistor and method for manufacturing thin film transistor

Abstract

(1) Disclosed is a thin film transistor comprising elements, namely a source electrode, a drain electrode, a gate electrode, a channel layer and a gate insulating film, said thin film transistor being characterized in that the channel layer is formed of an indium oxide film that is doped with tungsten and zinc and/or tin. (2) Disclosed is a bipolar thin film transistor comprising elements, namely a source electrode, a drain electrode, a gate electrode, a channel layer and a gate insulating film, said bipolar thin film transistor being characterized in that the channel layer is a laminate of an organic material film and a metal oxide film that contains indium doped with at least one of tungsten, tin or titanium and has an electrical resistivity that is controlled in advance. (3) Disclosed is a method for manufacturing a thin film transistor comprising elements, namely a source electrode, a drain electrode, a gate electrode, a channel layer and a gate insulating film, said method for manufacturing a thin film transistor being characterized in that at least the channel layer or a part of the channel layer is formed by forming a metal oxide film by a sputtering process using an In-containing target without heating the substrate, and a heat treatment is carried out after forming the above-described elements on the substrate.

1 . A thin film transistor comprising elements including three electrodes of a source electrode, a drain electrode and a gate electrode, as well as a channel layer and a gate insulating film, wherein the channel layer is formed of an indium oxide film doped with tungsten and zinc and/or tin. 
     
     
         2 . The thin film transistor according to  claim 1 , wherein the indium oxide film doped with tungsten and zinc and/or tin is formed by sputtering a target containing indium and tungsten and zinc and/or tin in a oxygen gas-containing atmosphere. 
     
     
         3 . The thin film transistor according to  claim 1 , wherein each of the elements is obtained by forming a film by sputtering without heating a substrate on which to form the film and without conducting an annealing treatment after the film formation. 
     
     
         4 . A bipolar thin film transistor comprising elements including three electrodes of a source electrode, a drain electrode and a gate electrode, as well as a channel layer and a gate insulating film,
 wherein the channel layer is a stack including   an organic material film, and   a metal oxide film which contains indium doped with at least one of tungsten, tin and titanium and which has an electrical resistivity that is preliminarily controlled.   
     
     
         5 . The bipolar thin film transistor according to  claim 4 , wherein the organic material film contains any of F8T2, P3HT, pentacene, and tetrabenzoporphyrin. 
     
     
         6 . The bipolar thin film transistor according to  claim 4 , wherein the channel layer has the metal oxide film and the organic material film stacked in this order from the side of the gate electrode. 
     
     
         7 . The bipolar thin film transistor according to  claim 6 , wherein the source electrode and the drain electrode are mounted in contact with the organic material film. 
     
     
         8 . The bipolar thin film transistor according to  claim 4 , wherein the metal oxide film contains not less than 0.5 wt % and less than 15 wt % of tungsten. 
     
     
         9 . The bipolar thin film transistor according to  claim 4 , wherein the electrical resistivity of the metal oxide film is 10 −1  to 10 4  Ωcm. 
     
     
         10 . A method for manufacturing a thin film transistor, comprising forming on a substrate an indium-containing metal oxide film in a predetermined pattern by sputtering conducted using an indium-containing target in an oxygen gas-containing atmosphere so that one or more elements including at least a channel layer or a part of the channel layer, of elements of the channel layer, a source electrode, a drain electrode and a gate electrode, are formed from the indium-containing metal oxide film,
 wherein the metal oxide film is formed by conducting the sputtering without heating the substrate, then the elements of the channel layer, the source electrode, the drain electrode and the gate electrode are formed over the substrate, and thereafter a heat treatment is conducted.   
     
     
         11 . The method for manufacturing the thin film transistor according to  claim 10 , wherein at least the channel layer or a part of the channel layer is formed by forming an indium oxide film doped with one or more of tin, titanium, tungsten and zinc through using as a target a sintered body of indium oxide doped with one or more of tin, titanium, tungsten and zinc. 
     
     
         12 . The method for manufacturing the thin film transistor according to  claim 11 , wherein at least the channel layer or a part of the channel layer is formed by forming an In—W—Zn—O film through using as a target a sintered body of In—W—Zn—O. 
     
     
         13 . The method for manufacturing the thin film transistor according to  claim 12 , wherein control of characteristics is conducted by regulating the W content and/or the Zn content of the sintered body of In—W—Zn—O used as the target. 
     
     
         14 . The method for manufacturing the thin film transistor according to  claim 11 , wherein a silicon wafer having a thermal oxide film to be a gate insulating film is used as a substrate functioning also as the gate electrode, an In—W—Zn—O film is formed on the thermal oxide film of the substrate by use of a sintered body of In—W—Zn—O as a target to thereby form the channel layer, and an ITO film is formed on the channel layer by use of a sintered body of ITO as a target to thereby form the source electrode and the drain electrode. 
     
     
         15 . The method for manufacturing the thin film transistor according to  claim 10 , wherein the heat treatment is conducted in air at 150 to 300° C. for 10 to 120 minutes.